Carburetor flooding or poor idle

Hard starting, fuel smell, rough idle, stalling. Sometimes floods and won't start at all.

SU carburetors (common on B18/B20) have needle valves, float bowls, and jets that gum up or wear out. Ethanol fuel accelerates varnish buildup. Float height drifts. Worn throttle shafts allow air leaks.

1. 1 Strip and rebuild the carbs. SU rebuild kits are cheap (~$40-60 per carb). Replace needles, seats, gaskets, diaphragms
2. 2 Check float height with a ruler: should be around 15-16 mm from gasket face to top of float (verify with your manual)
3. 3 Inspect throttle shaft play. If worn, you'll need new shafts or carb replacement
4. 4 Clean jets with carb cleaner and compressed air. Don't drill them out
5. 5 Ethanol-resistant fuel line and fresh fuel filter mandatory